Diesel fuel



Patented Oct. 3, 1939 UNITED STATES PATENT w OFFICE DIESEL FUEL No Drawing; Application October 8, 1937,

. Serial No. 167,93!

Claims.

This invention has to do in a general way with fuels for internal combustion engines of the Diesel type wherein ignition of the fuel is effected spontaneously bycompression in the cylinders 5 and is more particularly concerned with the modification of such fuels by incorporating therein characterizing ingredients for the purpose of controlling the combustion characteristics.

In the Diesel cycle internal combustion engine where the fuel is injected into the combustion space, it is important to the attainment of maximum efl'iciency that the delay period between injection and ignition be short. It will thus be' seen that enhanced speed of ignition is a highly desirable characteristic in fuels for this type of engine. Improperly delayed ignition in a Diesel engine gives rise to the phenomena known as knoc king due to improper coordination of combustion and cylinder characteristics,

It is therefore an important feature of this invention to decrease theignition delay period of Diesel fuel. This, in addition to eliminating the knocking above referred to, has the added advantage of giving a fuel in which combustion takes place at a lower compression pressure, increases the ease of starting, gives smoother operation and permits making the engine of less mass and consequently gives a lower cost per unit of power .output. a

It has been found that the ignition quality of a fuel oil can be improved by' the addition of small amounts of certain compounds which act as ignition accelerators. The addition of such accelerators offers a means for improving the -36 better grades of Diesel fuels and a means for widening the range of available fuels by raising the ignition quality of lower grades to a point where they can be satisfactorily used.

Several compounds have heretofore been sug- 40 geSted for this purpose and have been used with varying degrees of success. Some of these compounds are unsatisfactory from the standpoint of stability, cost, toxicity, or because of their tendency to form corrosive gases in the combustion 45 chamber of the engine.

Our present invention is predicated upon the discovery that the ignition quality of a Diesel fuel can be materially improved by incorporating a small quantity of diacetyl peroxide in the base 50 fuel stock and our invention contemplates as one of its objects a Diesel fuel having a minor proportion of diacetyl peroxide in admixture therewith in sufiicient amount to decrease the ignition delay period of the fuel. 55 Weare aware of the fact that certain peroxides have been proposed as blending ingredients for fuels for various purposes, but our present invention is directed primarily to a Diesel fuel having accelerated ignition quality and to diacetyl peroxide as the blending ingredient to effect such 5 increase.

Diacetyl peroxide is a well known organic compound having the formula of and various methods for its preparation can be found in the literature.

"'For example, diacetyl peroxide can be prepared by treating an ethereal solution of acetic anhydride with an aqueous suspension of barium 15 peroxide and recovering the product by careful evaporation of the ether. (See Clover and Richmond, Amer. Chem. Jour. 29, 182' (1903) and Freer and Novy, Amer. Chem. Jour. 27, 186 (1902).) This compound may also be prepared 20 from acetic anhydride and hydrogen peroxide in an ether extraction process. (See Nef., Ann. 298, 288 (1897)), or by treating an ethereal solution of acetic anhydride with moist sodium peroxide (see Gambarjan, Ber. 42, 4010 (1909) 5 The diacetyl peroxide prepared in accordance with any of the above methods may be isolated by careful evaporation of the ether solution and then dissolved in the Diesel fuel oil in the desired proportion. Since the preparation of the com- 30 pound in this way is a hazardous one involving the danger of explosion, we have devised another method of incorporating the diacetyl peroxide in the fuel which we consider preferable to the methods outlined above, and which is contemplated as a primary feature of our present invention.

In the practice of the preferred method contemplated by this invention, we first dissolve acetic anhydride in a solvent which is soluble in or miscible with the base fuel stock, and then form the diacetyl peroxide in this acetic anhydride solution by reaction with a suitable oxidizing agent such as barium peroxide in aqueous solutionvor suspension.

It is preferable to effect the conversion of the acetic anhydride to diacetyl peroxide, in this procedure, through the use of an inorganic peroxide, rather than by direct treatment with air or oxygen, since it provides means for conveniently controlling the reaction and the desired product is formed without appreciable attack on the fuel hydrocarbons. Furthermore, the use of an inorganic peroxide avoids the formation of acids, ketones and aldehydes, which would undoubtedly be formed if the conversion were effected by oxidation with air or oxygen and which would have to be renioved by refinement.

' ,The solvent for the acetic anhydride may be any suitable liquid which is also soluble in the base fuel stock, but we prefer to use some of the base fuel stock as the solvent or a fuel material similar thereto in character. If desired, the diacetyl peroxide may be formed in substantial concentration (say above 1% or 2%) in this initial solution, or it may be formed directly in the fuel at the concentration necessary to raise the ignition quality of the fuel to the desired point, generally less than 2%. In the first instance, the diacetyl peroxide solution will be blended with a base fuel stock and in the latter instance y no blending operation is necessary.

. found that the As a specific example of the method contemplated by this invention, a fuel blend containing diacetyl peroxide can be prepared as follows: A solution of 22 grams of acetic anhydride in 500 cc. of No. 2furnace oil was chilled to 20 F. with agitation. This solution was maintained within the temperature range of +20 to +30 F. and a suspension of 30 gramsofbarium perbxide in 30 cc. of water was slowly added thereto. This mixture was stirred for a period of two hours at reduced temperature, the precipitate was allowed to settle and the oil layer drawn off and dried over calcium chloride. The product consisted of 358 grams of .fuel oil solution containing 1.76% acetyl peroxide. The concentration of the peroxide in such a solution can be readily determined by known methods of analyses (for example see Marks and Morell Analyst 54, 503 (1929) A fuel oil solution of diacetyl peroxide of the type described above can be used as a Diesel fuel, such fuel having accelerated ignition characteristics. For most purposes, however, we have concentration of diacetyl peroxide "which will give the desired results is less than that obtained using the proporq tions of ingredients given in the above example, and where a.- relatively more concentrated solution such as that exemplified above is obtained,

such fuel-diacetyl peroxide solution may be blended with a base fuel stock to give a final fuel blend containing a lesser proportion of the diacetyl peroxide, but at the same time having substantialiy improved ignition quality. v

In conducting the tests which we have used to demonstrate the value of diacetyl peroxide, as an ingredient for accelerating the ignition quality of Diesel fuel, we have determined the ignition quality of the blended fuels by comparison with standard reference fuels in a converted CFR engine, using the ignition delay method. The results of these tests are expressed by cetane (or cetene) numbers. The cetane (or cetene) number is the percent by volume of cetane (or cetene) in a blend of cetane (or cetene) and alphamethyl naphthalene, which blended fuel has the same combustion characteristics as the sample being tested. (See Proc. Am. Soc. Testing Materials, V0. 36 I p. 418.) The increase in cetane (or cetene) number indicates a decrease in delay between fuel injection and fuel ignition and consequently indicates an improvement in fuel ,combustion characteristics.

As examples of the improved efficiency obtained through the use of diacetyl peroxide in Diesel fuel, we have indicated in the accompanying table the results of a plurality of tests showing the increase in cetane (or cetene) number obtained through the use of this compound in the same.

various types of base fuel stocks. In the table below, those values marked with an asterisk are cetene numbers. The cetene number differs from the cetane number only in that cetene is used as a standard instead of cetane and the increase in either cetane or cetene number indicates a comparative increase in the ignition quality of the blended fuel. Table I gives the physical characteristics of the different fuel stocks used in making the blends with diacetyl peroxide and Table II gives the results obtained through the use of various percentages of the diacetyl peroxide in these base fuel stocks and blends of such stocks.

Table I Stock A B C D Thermal Catalyti- Naturc Straight run No 2 cracked cally fuel 0 recycle cracked #3 stock. fuel oil.

Specific gravity l .861 0.89 0.89 Pensky Martens flash point 156 F. 140 F. 176 F. Aniline point. 132. 8 F. 94. 7 F. 10l.2 F. OolorLovibond 0. 25 105 11 Diesel index 43. 25. 3 27. 1 Octane number 53. 0 42. 0 40 30 Comm number.

Table II Cetane Cone. of Cetane Increase Base stock diacetyl g g z number in cetano peroxide of blend number stock 1. 0 '53. 0 67. 0 l4. 0 0. 99 42. 0 59:0 17. 0 0. 49 42. 0 51. 0 9.0 0. 19 42. 0 48. 5 6. 5 B 0. 09 42. 0 45. 5 3. 5 50-50 blend of B-l-C 0. 67 41. 5 49. 0 7. 5 50-50 blend of B+D 0.68 36.0 45.0 9.0

'Cetene number.

It will be observed from Table II above that diacetyl peroxide is efiective to materially increase the cetane number and therefore to materially improve the ignition quality of Diesel fuels when used in percentages ranging from 0.09% to 1.0%. It is to be understood of course that the percentage of diacetyl peroxide used in a blended fuel of this character may vary depending upon the type of base fuel stock used and the extent to which it is desired to improve This material may, for example, be used in amounts varying say from 0.05% up to or over approximately 2%, but for most purposes concentrations in the neighborhood of from 0.1% to 1.0% will give the desired results.

In the foregoing specification and in the followingclaims, the terms Diesel fuel, hydrocarbon fuel oil, liquid fuel, etc. include anyand all types of hydrocarbon products intended for use in any engine operating according to the Diesel cycle.

We claim:

1. The method of preparing an improved fuel oil for use in Diesel engines which includes the steps of dissolving acetic anhydride in a hydrocarbon oil suitable for use as a Diesel fuel and oxidizing the acetic anhydride in situ to diacetyl peroxide.

2. The method of preparing an improved fuel oil for use in Diesel engines which includes the steps of dissolving acetic anhydride in a hydrocarbon oil suitable for use as a Diesel fuel and adding an inorganic peroxide to'the hydrocarbon oil-acetic anhydride solution to convert the acetic anhydride to diacetyl peroflde.

3. The method of preparing animproved fuel oil' for use in Diesel engines which comprises:

dissolving acetic anhydride in a petroleum distillate suitable for use as a Diesel fuel and adding to said distillate-acetic anhydride solution an oxidizing agent which will convert the acetic anhydride to diacetyl peroxide, the proportions of said acetic anhydride and said oxidizing-agent being such that the diacetyl peroxide. will be formed in sufficient amount to decrease the ignioxidizing agent which will convert the acetic anhydride to diacetyl peroxide, the proportions of said acetic anhydride and said oxidizing agent being such that the diacetyl peroxide will be formed in an amount ranging from about 0.05

per cent to about 2.0 percent.-

5. The method of preparing an improved fuel oil for use in Diesel engines which includes the steps 'of: dissolving acetic anhydride in a hydrocarbon oil suitable for use as a Diesel fuel; adding 10 barium peroxide to said hydrocarbon oil solution in suflicient amount toconvert the acetic anhydride to diacetyl peroxide; and separating the precipitate from the diacetyl peroxide-hydrocarbon oil solution.

DARWIN E. IBADERTSCHER. GEORGE s. CRANDAIL. 

